01 - Preheat oven to 300°F (150°C). Line a baking sheet with parchment paper.
02 - In a clean mixing bowl, beat egg whites and cream of tartar with an electric mixer until soft peaks form. Gradually incorporate granulated sugar while beating until stiff, glossy peaks are achieved.
03 - In a separate bowl, whisk together egg yolks, cornstarch, and vanilla extract until the mixture is smooth and uniform.
04 - Carefully fold the prepared egg yolk mixture into the whipped egg whites using a spatula, ensuring the mixture remains airy and voluminous.
05 - Divide the batter equally among several bowls according to the desired colors. Add a few drops of gel food coloring to each and gently fold to achieve uniform coloration.
06 - Spoon dollops of colored batter onto the lined baking sheet, positioning them side by side to create a rainbow effect. For a marbled appearance, lightly swirl with a spatula.
07 - Bake in preheated oven for 25 minutes until set and lightly golden.
08 - Allow to cool briefly before transferring from the baking sheet. Serve immediately to enjoy maximum fluffiness.